The production of acetic acid by carbonylation of methanol and/or a reactive derivative thereof in the presence of a rhodium catalyst is described in, for example, GB 1,233,121, EP 0384652, and EP 0391680. The process in the presence of an iridium catalyst is described in, for example, GB 1,234,641, U.S. Pat. No. 3,772,380, EP 0616997, EP 0618184, EP 0786447, EP 0643034, EP 0752406.
Howard et al in Catalysis Today, 18 (1993), 325-354 describe the general rhodium and iridium-catalysed carbonylation of methanol to acetic acid. The continuous catalysed, homogeneous methanol carbonylation process is said to consist of three basic sections; reaction, purification and off-gas treatment. The reaction section comprises a stirred tank reactor, operated at elevated temperature, and a flash vessel. Liquid reaction composition is withdrawn from the reactor and is passed through a flashing valve to the flash vessel, in which a vapour fraction, comprising condensable components (including product acetic acid) and low-pressure off-gas, is separated from a liquid fraction. The vapour fraction is then passed to the purification section whilst the liquid fraction is recycled to the reactor. The purification section is said to comprise a series of distillation columns wherein impurities are removed from the acetic acid product.
EP 0685446 relates to a process for the preparation of acetic acid which comprises carbonylating methanol with carbon monoxide in a first reactor in the presence of a rhodium catalyst. The reaction fluid containing dissolved carbon monoxide is passed from the first reactor to a second reactor where the dissolved carbon monoxide, without the feeding of additional carbon monoxide, is further reacted before the reaction fluid is introduced into a flash zone.
EP 0846674 describes a liquid phase process for the production of carboxylic acid which comprises carbonylating an alkyl alcohol with carbon monoxide in a first reaction zone in the presence of an iridium catalyst wherein at least a portion of the liquid reaction composition together with dissolved and/or entrained carbon monoxide is withdrawn from the first reaction zone and is passed into a second reaction zone, and wherein at least a portion of the dissolved and/or entrained carbon monoxide in the withdrawn reaction composition is reacted by further carbonylation in the second reaction zone to produce further carboxylic acid product, prior to the reaction composition being passed into a flash zone.
WO 2009/103948 describes a process for the production of acetic acid by the carbonylation of methanol and/or a reactive derivative thereof with carbon monoxide in a reactor system comprising a first reaction zone, a second reaction zone, a flash separation zone, and one or more distillation zones to recover acetic acid product, wherein the temperature of the liquid reaction composition passed from the second reaction zone to the flash separation zone is at least 8° C. greater than the temperature of the liquid reaction composition withdrawn from the first reaction zone. The increase in temperature of the liquid reaction composition after its withdrawal from the first reaction zone prior to its passage into the flash separation zone can be achieved by the introduction of carbon monoxide into the second reaction zone, and/or the temperature increase could be achieved by applying heat to the second reaction zone.